U.S. Pat. No. 7,654,337 B2 discloses a control arrangement of this kind. This is used to control a drilling unit having a first hydraulic consumer in the form of a hydraulic hammering device and having a second hydraulic consumer in the form of a hydraulic feed device. The first consumer is connected to a variable displacement pump by a supply line. An electrically actuable selector valve for connecting and disconnecting the first consumer is provided in the supply line. A pressure reducing valve is arranged downstream of the selector valve, between said valve and the first consumer. In this arrangement, a valve body of the pressure reducing valve is acted upon in the open position thereof by a spring force of a valve spring and by a load sensing pressure dependent on the load pressure of the first consumer and is acted upon in the closed position thereof by the pressure downstream of the pressure reducing valve. The load sensing pressure is carried away via a load sensing line between the pressure reducing valve and the first consumer by way of a control oil nozzle. Downstream of the control oil nozzle, the load sensing line with the pressure reducing valve is connected—to subject the valve body to the load sensing pressure—to a pilot valve or pressure limiting valve for limiting the load sensing pressure and to one inlet of a shuttle valve.
A load sensing line of the second consumer is likewise connected to the inlet side of the shuttle valve. On the outlet side, the shuttle valve is connected to a load sensing regulating system of the variable displacement pump, as a result of which the highest load sensing pressure of the consumers is indicated to the load sensing regulating system by means of the shuttle valve. By means of the load sensing regulating system, a pump pressure of the variable displacement pump is matched to the highest load sensing pressure.
A hammering frequency of the first consumer, which is used as a hammering device, is dependent on the pressure prevailing at the consumer, for which reason, if the pump pressure is determined by the load of the second consumer (the feed device), this pump pressure is reduced by means of the pressure reducing valve to ensure that the pressure for the hammering device does not become too high.
With the control oil nozzle and the pilot valve, the pressure reducing valve is a pilot-controlled pressure reducing valve, on the valve body of which only very weak springs normally act. In order to allow a highly dynamic response from the control arrangement, the pump pressure is generally the result of the load sensing pressure together with a comparatively high pump Δp, which is 30 bar for example.
The disadvantage with this solution is that, in normal operation, in which the hammering device (first consumer) is the consumer with the highest load, the pressure reducing valve regulates a pressure corresponding to the difference between the pump Δp and the pressure equivalent of the spring force of the spring. Since the pump Δp, generally 30 bar, is significantly higher than the pressure equivalent of the spring force of the spring, which is 15 bar for example, the valve body of the pressure reducing valve is in a regulating mode between the closed and the open position thereof in normal operation of the control arrangement, and this leads to energy losses by the control arrangement.
Given this situation, it is the underlying object of the disclosure to provide a control arrangement which has extremely low energy losses in normal operation.
This object is achieved by a hydraulic load sensing control arrangement in accordance with the features described herein.
According to the disclosure, a hydraulic load sensing control arrangement has a first and second hydraulic consumer. A respectively highest load sensing pressure, which is dependent on the load pressure of each consumer, is indicated to a load sensing regulating system of a hydraulic pump supplying the consumers, in particular to a variable displacement pump. Provision is made here for the first consumer to have the highest load pressure in normal operation of the control arrangement. A pressure reducing valve is provided in the pressure medium flow path between the hydraulic pump and the first consumer. Said valve has a valve spool which can be subjected in the closing direction thereof to a pressure downstream of the pressure reducing valve and in the opening direction thereof to a regulating pressure dependent on the load pressure of the first consumer and to a spring force of a regulating spring. Here, a pressure equivalent of the spring force together with the regulating pressure is advantageously greater than a pump pressure in normal operation.
This solution has the advantage that the pressure reducing valve is completely open in normal operation, ensuring that energy losses due to the presence of the pressure reducing valve are extremely low here.
The regulating pressure can simply be tapped from the pressure medium flow path between the pressure reducing valve and the first consumer via a control line having a nozzle.
To limit the pump pressure in normal operation, the load sensing pressure of the first consumer is limited by means of a pressure limiting valve or pilot valve.
In an advantageous embodiment of the disclosure, the regulating pressure is the load sensing pressure of the first consumer, which is tapped downstream of the nozzle. This is then a conventional control arrangement, in which the spring force of the regulating spring is then adapted in such a way that, according to the disclosure, a pressure equivalent of the spring force together with the regulating pressure is greater than a pump pressure in normal operation.
The pressure equivalent of the spring force of the spring is preferably greater than a pressure difference between the pump pressure and the highest load sensing pressure of the consumers (=pump Δp). A high pump Δp leads to a highly dynamic response of the control arrangement, for which reason a comparatively large spring, e.g. one having a pressure equivalent close to 30 bar, is used for a high pump Δp.
In another embodiment, a second nozzle is provided downstream of the first nozzle in the control line. Here, the nozzles form a pressure divider, in which case the regulating pressure for the pressure reducing valve is then tapped in the flow path between the nozzles. A pressure downstream of the second nozzle is then the load sensing pressure of the first consumer. Thus, a magnitude of the regulating pressure is between the load pressure of the first consumer and the load sensing pressure thereof. In comparison with an embodiment of the control arrangement with just one nozzle, the regulating pressure is thus higher, for which reason the spring force of the regulating spring can be smaller to ensure that, according to the disclosure, a pressure equivalent of the spring force together with the regulating pressure is greater overall than the pump pressure in normal operation. A lower spring force leads to a smaller spring, which requires a small installation space and is simple to install owing to the lower spring forces.
The pressure divider is preferably designed in such a way that, in the regulating mode of the pressure reducing valve, in which the first consumer is not the consumer with the highest load pressure, the pressure drop across the nozzles between a pressure tap of the control line downstream of the nozzles and an inlet of the pressure limiting valve, together with the pressure equivalent of the regulating spring, is greater than the pressure difference between the pump pressure and the highest load sensing pressure of the consumers, i.e. the pump Δp. This has the effect that a load pressure of the first consumer does not rise, despite a load pressure of the second consumer exceeding the load pressure of the first consumer.
It is advantageous if the pressure reducing valve is designed simply as a pressure compensator, which generally has large regulating springs, e.g. with a pressure equivalent of a spring force of 15 bar.
The control arrangement is preferably used to control a hydraulic drilling unit, in which case the first consumer is then a hammering device, which is dependent on the prevailing pressure, and the second consumer is a feed device.
A control valve, in particular in the form of a logic valve, is simply provided in the pressure medium flow path between the pressure reducing valve and the first consumer to connect and disconnect the first consumer.